The invention relates to apparatus and methods for manufacturing capacitors and for mounting capacitors on motors and other equipment.
Large capacitors of the type having a cylindrical or oval canister are typically installed on motors, power supplies, lighting fixtures, and other equipment using special covers or brackets. For example, capacitors are installed on the outside of motors using a xe2x80x9cdog housexe2x80x9d cover made from sheet metal. The capacitor canister is inserted into the open side of the cover, and held in place by protrusions matching the shape of the canister. The cover, with canister installed, is then screwed down to the motor housing. One such cover is shown in U.S. Pat. No. 3,030,532. Metal or plastic straps are also used; a strap extends around the body of the capacitor canister, and its ends are fastened to the equipment to which the capacitor is being attached.
Typically, capacitor canisters are manufactured in a relatively small range of sizes and shapes, and the equipment manufacturer is responsible for custom designing the dog house, strap, or installation brackets to adapt one of the canister shapes to its particular equipment. The capacitor canister is often made from polymer (e.g., polypropylene).
We have discovered a simpler, lower-cost way of installing polymer capacitor canisters on motors and other equipment. A bracket and/or fastener is attached to the canister (e.g., by ultrasonic welding a polymer fastener or bracket directly to the polymer canister), and the fastener and/or bracket are used to make the connection between the canister and the equipment. E.g., fasteners may be chosen so that they mate with holes or matching fasteners on the equipment to which the capacitor is being attached. Depending on choice of fastener, installation of the capacitor becomes a simple snap-in action. The capacitor manufacturer can now easily manufacture capacitors with a wide range of built-in fastener arrangements, relieving the equipment manufacturer of most of the work formerly associated with installing a capacitor on equipment.
In a first aspect, the invention features a capacitor with a polymer canister comprising a polymer wall surrounding a capacitive element. In one configuration, at least one fastener is supported on the exterior surface of the polymer wall. The capacitor fastener is configured to attach the canister to the equipment in which the capacitor is to be installed. Alternatively, a bracket may be adhered (e.g., by ultrasonic welding) to the exterior surface of the polymer wall, and the bracket configured to support a fastener.
One or more of the following features may preferably be used in preferred embodiments of this aspect of the invention. A bracket may be provided with openings for receiving fasteners extending from the equipment (instead of providing the fasteners on the canister). The fastener may be a male fastener and be attached to the bracket prior to installation of the capacitor in the equipment. The fastener may be a female fastener configured to mate with a male fastener attached to the equipment. The bracket may have at least one hole through which the at least one fastener extends, and the bracket may have a cavity on its rear surface (which faces the canister wall), and the cavity may be sized and configured to hold the head of the fastener. The canister may have at least one curved surface, and the bracket may be adhered to the curved surface. The canister may be approximately cylindrical (circular or oval in cross section), the bracket may be elongated, and the long dimension of the bracket may run in the longitudinal direction of the cylinder. The bracket may be ultrasonically welded to the canister wall. The bracket and polymer may be made primarily of polypropylene. The bracket may have an opening for receiving a fastener configured to clamp the bracket to the equipment. The bracket may have a slot with a variable radial distance from the centerline of the canister, and the slot may be configured to receive a fastener and to cause the fastener to be forced radially against the wall of the slot when the canister is rotated about the centerline to move the fastener along the length of the slot. At the end of the slot at which the slot is radially closest to the centerline of the canister, the slot may be wider than at the other end, thereby easing reception of the fastener within the slot. At least one resilient element (e.g., a wing-like extension) may be included on the bracket, with the element being configured to press against the equipment when the capacitor is installed to reduce vibration.
In a second aspect, the invention features a method of manufacturing capacitors of the type in which a capacitive element is housed in a polymer canister, which is, in turn, installed in equipment. The capacitors are manufactured with canisters of a small number of sizes and shapes. The manufactured capacitors are stored in inventory without attaching fasteners for attaching the canister to the equipment. A specification is received of the type, location, and size of fastener that an equipment manufacturer desires to use to attach the canister to the equipment. The manufactured capacitors are removed from inventory, and the fasteners as specified are attached to the canister.
One or more of the following features may preferably be used in preferred embodiments of this aspect of the invention. The fasteners may be connected to the canister by adhering a bracket to the canister, with the bracket providing support for the fasteners. Different sizes and types of fasteners may be used with the same bracket.
Other features and advantages of the invention will be apparent from the following description of preferred embodiments and from the claims.